Spacetime and the philosophical challenge of quantum gravity

Butterfield, Jeremy; Isham, C. J.

doi:10.1017/cbo9780511612909.003

Cited by 139 publications

(135 citation statements)

References 37 publications

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“…The key point now is that from the later data (14) at any time t > t * you cannot determine the initial data (v 0 , x 0 ), nor even the time t * when the object came to rest, thus you cannot reconstruct the trajectory (13) from that later data. You cannot even tell if the block came from the left or the right.…”

Section: Irreversible Dynamicsmentioning

confidence: 99%

Spacetime and the Passage of Time

Ellis

Goswami

2014

Springer Handbook of Spacetime

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This paper examines the various arguments that have been put forward suggesting either that time does not exist, or that it exists but it's flow is not real. I argue that (i) time both exists and flows; (ii) an Evolving Block Universe ('EBU') model of spacetime adequately captures this feature, emphasizing the key differences between the past, present, and future; (iii) the associated surfaces of constant time are uniquely geometrically and physically determined in any realistic spacetime model based in General Relativity Theory; (iv) such a model is needed in order to capture the essential aspects of what is happening in circumstances where initial data does not uniquely determine the evolution of spacetime structure because quantum uncertainty plays a key role in that development. Assuming that the functioning of the mind is based in the physical brain, evidence from the way that the mind apprehends the flow of time prefers this evolving time model over those where there is no flow of time. Space time and the Block UniverseIn this section I briefly summarize the usual representation in relativity theory of space-time as an unchanging block universe, and the associated view that the change of time is an illusion.The nature of spacetime in both special and general relativity has lead some to a view that the passage of time is an illusion [72,12,39,40]. Given data at an arbitrary time, it is claimed that everything occurring at any later or earlier time can be uniquely determined from that data, evolved according to deterministic local physical laws (this is formalized in standard existence and uniqueness theorems [49]). Consequently, nothing can be special about any particular moment; there is no special "now" which can be called the present. Past, present and future are equal to each other, for there is no surface which can uniquely be called the present.Such a view can be formalized in the idea of a Block Universe [59,70,17]: space and time are represented as merged into an unchanging spacetime entity, with no particular space sections identified as the present and no evolution of spacetime taking place. The universe just is: a fixed spacetime block, representing all events that have happened and that will happen. This representation implicitly embodies the idea that time is an illusion: time does not "roll on" in this picture. All past and future times are equally present, and the present "now" is just one of an infinite number. Price [67] and Barbour [7] in particular advocate such a position. Underlying this, as emphasized by Barbour, is the idea that time-reversible Hamiltonian dynamics provides the foundation for physical theory in general and gravitation in particular. Occasionally cosmology or astrophysics takes into account time-irreversible physics, for example nucleosynthesis in the early universe or the late phases of gravitational collapse, but the notion of the present as a special time remains absent.The problem with this view is that it is profound contradiction with our experiences in e...

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Section: Irreversible Dynamicsmentioning

confidence: 99%

Spacetime and the Passage of Time

Ellis

Goswami

2014

Springer Handbook of Spacetime

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“…These are outlined in a number of places. The following list is compiled from (Wald 1994) and (Butterfield and Isham 2001).…”

Section: Problems Of Theorymentioning

confidence: 99%

Is Quantum Gravity Necessary?

Mattingly

2005

The Universe of General Relativity

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Quantum gravity presents something of a unique puzzle for the philosophy of science. For in a very real sense, there is no such thing as quantum gravity. Despite near unanimous agreement among physicists that a quantum theory of gravitation is needed to reconcile the contradictions between general relativity and quantum mechanics, there are no pressing empirical issues that require this resolution-the regime in which one would expect to observe a conflict between the claims of general relativity and quantum mechanics is at the Planck scale. Thus the question naturally arises "Why quantize gravity?" Are there other issues that compel us to seek a quantum theory of gravity?The standard response is intimately connected with a desire for theoretical unification. Quantum field theory successfully describes the physical world on small length scales at low "particle" density. General relativity is a successful theory of large length scales where individual features of particular objects are swamped by their mass-energy properties. It is natural to seek a unified theory that captures these successful features and yet is somehow a "fundamental" theory of both regimes. But why should the resulting theory involve a quantized gravitational field? There is clearly something wrong with the general relativistic treatment of matter fields as classical. Very well. Let us stipulate that an acceptable theory of gravitation will take due note of the quantum nature of the fields to which it couples. Now what? Are we thus compelled to treat the gravitational field itself quantum mechanically?There are a number of arguments urging the necessity of a full quantum gravity-i.e., a theory of gravity that treats the metric itself as a quantum field. There are, as well, a number of proposals for how we should go about producing this theory. I will not here be concerned to articulate the panoply of attempts to quantize gravitation theory (nor to elaborate the many prob-

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“…One could try to choose a specific gauge in accordance to the invariance associated with the algebra (3.8)-(3.10), then solve the constraints (3.4) and (3.5), and finally quantize the resulting system with the "true" degrees of freedom. It turns out that in general the final equations are tractable only perturbatively, and lead to ultraviolet divergences (for further details see, for example, [13,14]). …”

Section: Time In General Relativitymentioning

confidence: 99%

Time Paradox in Quantum Gravity

Macı́as

Quevedo

Quantum Gravity

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Abstract. The aim of this work is to review the concepts of time in quantum mechanics and general relativity to show their incompatibility. We show that the absolute character of Newtonian time is present in quantum mechanics and also partially in quantum field theories which consider the Minkowski metric as the background spacetime. We discuss the problems which this nondynamical concept of time causes in general relativity that is characterized by a dynamical spacetime. Mathematics Subject Classification (2000). Primary 46N50; Secondary 85A99.

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Spacetime and the philosophical challenge of quantum gravity

Cited by 139 publications

References 37 publications

Spacetime and the Passage of Time

Spacetime and the Passage of Time

Is Quantum Gravity Necessary?

Time Paradox in Quantum Gravity

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